Electronic Packages and Components Thereof Formed by Co-Deposited Carbon Nanotubes

ABSTRACT

Microelectronic packages may be formed using the co-deposition of carbon nanotubes. The carbon nanotubes may be functionalized to have an appropriate charge so they can be combined with other materials to give suitable properties. The other materials that are co-deposited may include metals, ceramics, and polymers. The electronic package components may be formed including thermal interface materials, vias, trenches, capacitors, memories, substrates, and substrate cores, as a few examples.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/633,821, filed on Dec. 5, 2006.

BACKGROUND

This relates generally to electronic packages and, particularly, topackages for integrated circuit chips such as microprocessors.

Integrated circuit packages connect to contacts on an integrated circuitchip. The integrated circuit package, in turn, provides connections tothe chip through the package. Because of the large number of inputs andoutputs that may be involved and, in some cases, the high frequenciesinvolved, there are numerous complexities in forming integrated circuitpackages. Ideally, to obtain the greatest possible speed it is desirableto have relatively low resistance packaging. This means that a largenumber of connections can be made with relatively little resistance.

Conventional integrated circuit packages are made of conductors formedof metals. Generally, these metals are limited in terms of conductivity.Moreover, with existing metals, certain thermal dissipation may beachieved, but there are limits to those possible thermal dissipationsinherent in the type of material. Likewise, the metal materials have agiven strength for a size at which they are deposited, but, again, thissize is relatively limited by the nature of the metals used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged, cross-sectional view of an electronic package inaccordance with one embodiment of the present invention;

FIG. 2 is a depiction of an electrolytic bath in accordance with oneembodiment of the present invention; and

FIG. 3 is a system depiction.

DETAILED DESCRIPTION

Referring to FIG. 1, an integrated circuit electronic package 10 mayhave superior properties by virtue of the use of co-deposited carbonnanotubes. That is, carbon nanotubes may be deposited to form variousstructures of the package 10. Carbon nanotubes may have, in givenapplications, superior properties to those achievable with conventionalmetals. For example, carbon nanotubes may have superior mechanicalstrength, superior conductivity, or superior thermal conductivity.

In order to achieve the desired results, the carbon nanotubes may beco-deposited with another material. The materials that may beco-deposited may include at least the following general types: metals,polymers, and ceramics.

As non-limiting examples, co-depositions of a metal with carbonnanotubes may be used to form thermal interface materials, silicontrenches, and vias for sensors and interconnect applications, first andsecond level package interconnects, substrate vias and trenches,interconnects, and memory cells. Co-deposition of polymers with carbonnanotubes may be used to make substrate cores with high strength carbonnanotube based epoxy composites, ultra-thin capacitors with carbonnanotube interconnect terminals, carbon nanotube polymer composites forhigh adhesion surfaces where the projecting carbon nanotubes act asmechanical entanglements, conducting polymer carbon nanotubesinterconnects based on polyaniline and carbon nanotube components asbond/electrode pads for low end applications requiring ultra smallinterconnects. Composites of ceramics and carbon nanotubes may be usedfor magnetic nanoparticles with the carbon nanotubes offering conductingproperties for magnetic memories and electromagnetic switches inmicroelectromechanical devices.

The nanotube electrodeposition may be done by electroplating,electroless plating, or electrophoresis, as examples. Selectivity ofdeposition of nanotubes and their composites may be achieved by maskingunwanted areas of electrodes with Teflon or photoresist polymer such aspolymethylmethacrylate (PMMA). Electrodeposition of nanotubes in thecase of composites may be via electrodeposition owing to the charge onthe nanotubes and adsorption of the nanotubes due to their high surfaceenergy.

Electroless plating may be used where nanotubes need to be co-depositedwith other materials. The co-deposited metals, such as nickel or copper,may be plated by electroless plating. The nanotubes are plated purelydue to surface absorption along with the nickel. This process may haveapplications in second level thermal interface materials insemiconductor packages.

Electrophoresis may be utilized for selective deposition of nanotubes insilicon trenches, or microelectric substrate trenches. Electrophoresisworks for deposition of pure nanotubes, as well as for co-depositions ofnanotubes with metals, polymers, or ceramics. Particularly, copper andcarbon nanotube composites may be formed, for example.

Vapor grown carbon nanotube nanofibers formed by a catalyst assistedchemical vapor deposition may be deposited by electroplating. The carbonnanofiber filler may have a diameter of 100 to 200 nanometers or lower,the fibers being about 20 microns long. A base plating bath of sulfuricacid may be used, together with polyacrylic acid, with mean molecularweights of 5000 and 25,000 to aid in dispersion of the fibers in thebath in one embodiment. Aeration under galvanic conditions may be usedat temperatures of 25° C. Pure copper and stainless steel plates withexposed surface areas may be used as the substrates. A phosphoruscontaining copper plate may act as the anode.

Electrophoresis deposition may be done by mixing 60 weight percent ofsingle walled carbon nanotubes in 200 milliliters concentratednitric/sulfuric acid solution for a few minutes. The suspension may berefluxed with magnetic stirring at 100 to 120° C. for a few hours. Thesuspension may then be filtered and the wet powder cleaned withdistilled water and dried at room temperature. The powder may then bemixed with distilled water during sonication. A surface charge may beapplied to the particle by adding 10⁻⁶ to 10⁻² mole of Mg(NO₃)₂6H₂O.Carbon nanotubes may be patterned onto metal cathodes with a negativebias of 10 to 50 volts DC applied to a patterned metal plate.

Continuing with FIG. 1, the package 10 may include a substrate 12coupled to a substrate core 16. Thus, thermal vias 14 may extend throughthe substrate 12, including its core 16. Also formed on the substratemay be capacitors or dynamic random access memories 18.

Formed on the substrate may be an integrated heat spreader 26 whichencloses an integrated circuit having solder balls 28 to couple itelectrically and mechanically to the substrate 12. The integratedcircuit may include vias 14 through the silicon known as through siliconvias (TSVS) 20. The integrated circuit may also include a silicondynamic random access memory or integrated voltage regulator 22. Theintegrated circuit itself may, for example, be a microprocessor. A firstthermal interface material 24 may couple the integrated circuit to anintegrated heat spreader 26.

Various materials may be co-deposited with nanotubes. The nanotubes mayeither be pristine or functionalized with one or more functional groups.Thus, pristine nanotubes are not functionalized as used herein andfunctionalized carbon nanotubes are nanotubes reacted with anothermaterial which has either a positive or negative charge. As a result ofthe reaction with another material, the nanotubes become electricallycharged and charged nanotubes are described herein as functionalized.

For example, nanotubes may be reacted with a carboxyl or OH group toform negatively charged functionalized carbon nanotubes. Carbonnanotubes may be reacted with an amine to form positively charged carbonnanotube groups. The carbon nanotubes may be deposited by themselves orwith metals or ceramics or polymers. Useful polymers includepolyaniline, epoxy, and polyimide. Ceramics may include silica. Metalsmay include solder, copper, and gold. Thus, the composite may include afunctionalizing agent to provide a charge, together with a material tobe deposited with the carbon nanotube or only the carbon nanotubesthemselves.

Pristine carbon nanotubes may be electroplated using an electrolyticbath as shown in FIG. 2. The electrolytic bath may include anelectrolytic solution 30 with one or more solvents, such as sulfuricacid, copper sulfate, nitric acid, acetone, or toluene, to mention a fewexamples. Pristine or functionalized nanotubes are dispersed in thesesolvents with appropriate functionalizations. The nanotubes may beelectrodeposited onto anode or cathode 32, depending on theirfunctionalized charge. Although pristine nanotubes are known to beelectron donors, the nanotube surface charge and polarity can betailored by functionalization. The electrode surface may, for example,be pure silicon, Integrated Heat Spreader (IH-S), or organic or ceramicsubstrates, depending on the application.

Co-deposition of metal with carbon nanotubes may be achieved bydispersing the carbon nanotubes in electrolyte solution such as sulfuricacid. The carbon nanotubes may be functionalized with carboxyl or thiolgroups which are suitable for bonding with metals and then dissolved inan acid bath. Metals such as solder or copper may also be dissolveddirectly into the same bath, for example, with sulfuric acid and thenco-deposited along with the nanotubes. Suitable solders include indiumor tin or tin silver alloys or tin silver copper alloys, to mention afew examples.

Carbon nanotubes or carbon nanotube metal functionalized structures maybe co-deposited with metals in the electrolytic bath onto electrodes.The choice of electrode depends on the charge of the carbon nanotubefunctionalization. The electrodes may be Integrated Heat Spreader(IH-S), silicon, or any other conductive surface used formicroelectronic packaging applications.

The co-deposition of a carbon nanotube with ceramic material may involvethe use of silica, alumina, zirconia, or magnetic iron oxide,functionalized with ionic groups such as alkyl sulfonate and potassium,R(OCH₂CH₂)₇—O—(CH₂)₃SO₃ ⁻K⁺, where R is the alkyl chain C₁₃H₂₇ toC₁₅H₂₉. These particles may be directly dispersed into the electrolyticacid bath. Pristine or functionalized carbon nanotubes may be dispersedin that bath. The functionalized ceramic nanoparticles and carbonnanotubes may then be co-deposited onto an electrode, suitable for theparticular packaging application.

Carbon nanotubes may be co-deposited with polymers, including bothconducting and non-conducting polymers. Examples of conducting andnon-conducting polymers include, but are not limited to, conductingpolymers with polyaniline or poly-m-phenylene vinylene or polyethyleneoxide. Non-conducting polymers may include epoxies or polyimides.Aniline monomer may be dissolved into a sulfuric acid bath to beco-deposited along with negatively charged carbon nanotubes on asuitable electrode. Epoxy or non-conducting polymers may be chemicallybonded to water soluble functional groups or radicals, such as silanes,and then dissolved in the acid bath.

The non-conducting polymers can also be attached to nanotube surfacesvia amine functionalization prior to the dispersion of the latter intoelectrolytic solvents. The amine functionalization may be by acidreflux, together with ammonium plasma of carbon nanotubes. Theco-deposition of carbon nanotubes and epoxy or other non-conductingpolymers can occur purely by statistical probability of nanotubeadsorption onto the electrode surface owing to the high surface energyof nanotubes.

Thus, the substrate 12, shown in FIG. 1, may be formed of high strengthcarbon nanotube based epoxy composites. The thermal via 14 may be formedby a metal carbon nanotube composite. The capacitors or dynamic randomaccess memories 18 may also be made by metal carbon nanotubeco-deposition. The capacitors and memories 18 may also be made of carbonnanotube electrodes with magnetic ceramics or metals. The throughsilicon via 20 may be made of a carbon nanotube metal co-deposition suchas a carbon nanotube/copper composite for high current densityapplications. The thermal interface material 24 may be made of carbonnanotubes and polymers or carbon nanotubes and metal composites. Thesubstrate core 16 may be made of carbon nanotube polymer composites frommechanical stability including high structural strength, low coefficientof thermal expansion, and high stiffness.

In some embodiments, electro co-deposition of carbon nanotubes andnanotube composites may offer advantages in terms of scalability,structural stability, selectivity, and enhancement of properties such asthermal conductivity, coefficient of thermal expansion, or electricalconductivity owing to interface tailoring and dispersion. The processesmay be implemented, in some embodiments, near room temperature andthereby are compatible with packaging applications. Also, an electroco-deposition process may enable the use of existing scalableinfrastructure, such as electroplating baths used for high volumesilicon processing, in some cases.

Suitable nanotubes may have low coefficients of thermal expansion, forexample, about 10⁻⁶/K, high thermal conductivity, for example, 3000 W-mKor higher, high current carrying capacity (approximately 10⁹ A/cm²), andhigh surface area due to high aspect ratios greater than 1000. Due tosuch unique structure and property characteristics, nanotubes may have arange of applications in microelectronic packaging including thermalinterface materials, interconnects, vias, substrate trenches,microchannel walls for enhanced fluid wicking, reversible adhesivestructures for mobile thermal interface materials, high strengthcomposites for substrates, and substrate cores.

Referring to FIG. 3, in accordance with some embodiments of the presentinvention, a computer system 40 may be formed using the package 10 shownin FIG. 1. Particularly, a packaged processor may be coupled by a bus 34to various other components such as dynamic random access memory (DRAM)44, input/output (I/O) devices 38, and static random access memory(SRAM) 36. A suitable power supply 42 may supply power to the processor10 and the other components.

In some embodiments of the present invention, any processor-based systemmay be formed. Thus, the embodiment shown in FIG. 3 is merely anexample. By improving the power delivery network performance, theperformance of an integrated circuit at high frequencies may beimproved. In some embodiments, this may be done at relatively low costand with relatively low process complexity.

References throughout this specification to “one embodiment” or “anembodiment” mean that a particular feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneimplementation encompassed within the present invention. Thus,appearances of the phrase “one embodiment” or “in an embodiment” are notnecessarily referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be instituted inother suitable forms other than the particular embodiment illustratedand all such forms may be encompassed within the claims of the presentapplication.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed is:
 1. A method comprising: forming a microelectronicpackage using co-deposition of carbon nanotubes and another material. 2.The method of claim 1 including functionalizing said carbon nanotubes.3. The method of claim 2 including co-depositing functionalized carbonnanotubes with a metal.
 4. The method of claim 2 including co-depositingfunctionalized carbon nanotubes with a polymer.
 5. The method of claim 2including co-depositing functionalized carbon nanotubes with ceramic. 6.The method of claim 1 including co-depositing the carbon nanotubes in anelectrolytic bath.
 7. The method of claim 1 including using selectiveco-deposition of carbon nanotubes.
 8. The method of claim 1 includingco-depositing carbon nanotubes with a conductive material.
 9. The methodof claim 1 including co-depositing carbon nanotubes with anon-conductive material.
 10. The method of claim 1 includingco-depositing carbon nanotubes in a depression in a substrate.